scharbit,
There's no hotline, other than AppleCare, that I know of, so we're pretty much on our own. From your error message, I'd guess that you're using the wrong domain name. The external domain name is usually different that what you would see in looking at your Outlook account settings.
One of the usual formats, though your Admins can pretty much call it anything they want to, is to add 'mail.' to the front of your external domain, i.e. if your email address is jane.doe@mycompany.com, your email server's external domain name would be mail.mycompany.com Is that what you're using? If not give it a try.
Also, as I mentioned above, you may need to add your internal domain name to your user ID in your iPhone's account settings. You can find this by right-clicking on the My Computer icon on your desktop or in your Start menu and selecting Properties. From there, click on the Advanced tab and then click on the Settings button in the middle under User Profiles. Be patient, as it may take a few moments for the User Profiles window to come up. When it does, find your user name and the domain name will be everything to the left of the backslash in front of your user ID. If you find your username in the list twice, one of them will likely be your computer's name. You can try both in your iPhone as the wrong domain name won't hurt anything. Be sure to Cancel out of the User Profiles and System Properties windows so that you don't change any settings.